THE first hearings into the calamitous Edinburgh tram project are set to take place this September - more than three years after Lord Hardie was appointed to spearhead the inquiry.

Sessions for gathering oral evidence are expected to span "several months" but critics have warned the hearing could amount to a "show trial" attributing blame for the fiasco to those who have already "left the scene".

The Edinburgh tram project was originally forecast to cost £375 million and be completed by 2009 when it was first suggested in 2003.

But by the time it was finally finished in 2014 it had cost taxpayers £776m, with trams running along a much shorter route than initially planned.

Lord Hardie has gathered six million documents and has yet to call any witnesses to give evidence in public - or set a publication date for its final report.

But veteran trams critic and former engineer John Carson said: "Lord Hardie has been working behind the scenes for some time and has been swamped with paperwork. I suspect those in the inquiry already know where the skeletons are and all that's left is the show trial.

"But many of the culprits have long gone with their pensions. But those who not been exposed are the politicians and those in government agencies."

A transport source within at Edinburgh City Council said officials have been “staggered” by how long it has taken the inquiry to begin accepting oral evidence.

One said: “I don’t think it’s been well organised. There have been some witnesses that have been in there for five days – often being asked questions about issues that took place years before their involvement in the project.

“They are being asked hundreds of questions lasting hours, and I don’t think they are all relevant or concentrating on the key issues. It is staggering that it has taken so long to begin oral hearings.”

The source added that they expect Lord Hardie to rule on the inquiry at the end of 2018.

The inquiry into the handling of the project was launched in 2014 by then First Minister Alex Salmond. It was initially non-statutory, meaning there was no legal authority to compel witnesses to attend, but was later upgraded to ensure key personnel would provide evidence.

It has been claimed that inquiry costs had reached almost £5 million by the end of September and that the Scottish Government's spending plans for 2017-18 set the inquiry's budget for the year at a further £1.5m.

Evidence at the hearings be given by a number of witnesses who will be cited to appear and will supplement written statements millions of documents already recovered during the course of investigations by the inquiry team.

Lord Hardie said the announcement that oral evidence would now be heard marks a milestone in the inquiry's progress.

He said: "The oral hearings form an essential part of the important work of the inquiry and the evidence heard will play a crucial role in informing my final recommendations.

"In advance of these hearings, a significant amount of activity has already taken place including identifying, retrieving and reviewing more than six million documents and the ongoing gathering of statements from a significant number of witnesses."

Lord Hardie has vowed to provide "robust recommendations" to ensure future infrastructure projects avoid the problems experienced by the scheme.

In a newspaper column yesterday former SNP MSP and Government minister Kenny MacAskill said he expected "a few minions to be sacrificed" in the inquiry but that "the political mistakes will be passed by".

Alison Bourne, who was a formal objector to the tram project throughout the Edinburgh City Council and Scottish Parliament scrutiny process, welcomed the timetable for the hearings to commence.

She added: “I’ve been so far quite impressed with the inquiry team’s thoroughness. They seem to be asking the correct questions and that has given me the confidence to submit evidence. I have to be optimistic about the process as it’s the only way by which measures may eventually be put in place to protect the taxpayer against similar mistakes in future.”